The present invention relates to a double-wall-tube heat exchanger and, more particularly, to a double-wall-tube heat exchanger which has an outer tube, and an inner tube provided in and spaced apart from the outer tube.
Herein, the term “condenser” refers to not only an ordinary condenser but also a subcooling condenser, which has a condensing section and a supercooling section.
A conventionally proposed refrigeration cycle for use in a car air conditioner includes a compressor; a condenser having a condensing section and a supercooling section; an evaporator; an expansion valve serving as a pressure-reducing device; a vapor-liquid separator; and an intermediate heat exchanger disposed between the condenser and the evaporator and adapted to perform heat exchange between a high-temperature refrigerant from the supercooling section of the condenser and a low-temperature refrigerant from the evaporator (see Japanese Patent Application Laid-Open (kokai) No. 2006-162238). In the refrigeration cycle described in the publication, the refrigerant which has been supercooled in the supercooling section of the condenser is further cooled in the intermediate heat exchanger by the low-temperature refrigerant from the evaporator. By this procedure, the cooling performance of the evaporator is improved.
The intermediate heat exchanger used in the refrigeration cycle described in the above-mentioned publication is a double-wall-tube heat exchanger which has an outer tube, and an inner tube disposed in and spaced apart from the outer tube. A clearance between the outer tube and the inner tube serves as a high-temperature refrigerant flow path through which the high-temperature refrigerant from the condenser flows, and the interior of the inner tube serves as a low-temperature refrigerant flow path through which the low-temperature refrigerant from the evaporator flows. Opposite end portions of the inner tube project from opposite end portions of the outer tube. Expanded portions are formed on the outer tube near the opposite ends thereof. A refrigerant inflow pipe which communicates with the refrigerant flow path between the outer tube and the inner tube is connected to one expanded portion, and a refrigerant outflow pipe which communicates with the refrigerant flow path between the outer tube and the inner tube is connected to the other expanded portion. Contracted portions are formed on the outer tube to be located on the outer sides of the expanded portions without respect to the longitudinal direction thereof, and are brazed to the inner tube.
Incidentally, in the case where the refrigeration cycle described in the above-mentioned publication is used in a car air conditioner, in some cases, an intermediate portion of the intermediate heat exchanger with respect to the longitudinal direction thereof must be bent at least one location in order to reduce a required install space of the intermediate heat exchanger in the engine compartment of an automobile. However, at the bent portion, the outer tube deforms, and the high-temperature refrigerant flow path collapses, so that its cross sectional area decreases, which raises a problem of increased pressure loss.
In the case of the double-wall-tube heat exchanger described in the publication, the groove portions of the inner tube not only increase the heat transmission area between the refrigerants flowing through the two flow paths, but also prevent collapse of the high-temperature refrigerant flow path at the bent portion, which collapse would decrease the cross sectional area of the high-temperature refrigerant flow path.
However, since the groove portions of the inner tube of the double-wall-tube heat exchanger described in the publication are formed by means of performing additional work on a manufactured inner tube over a relatively wide area so as to deform the tube wall, the conventional double-wall-tube heat exchanger has a problem in that the additional work is troublesome.